1. Field of the Invention
This invention relates to audio and visual warning and alarm systems and particularly to warning and alarm systems adapted to communicate prior to when a dangerous voltage is present on the third rail of a transit or railroad system.
2. Description of the Prior Art
The intent of this invention is to provide personnel with a non-hazardous warning system prior to third rail energization with 625 volts D.C.
Currently there exist two indication methods of third rail energization which are hazardous to personnel working on tracks. These two methods can be used separately or in conjunction with each other. The first method being a bank light device, hence its name Bank Light Device. This device consists of a set of five 125 volt incandescent bulbs that are wired in series and connected to the third rail by means of alligator clips. The second warning method is an audio-visual device. This device is also activated by a 625 volt D.C. and is connected in the same fashion as the bank light device. In both cases a dangerously high voltage is required to activate these indication devices. There is no prior warning of 625 volt D.C. energization to track personnel.
The typical transit system will have two running rails on which the wheels of the cars roll and a third rail which carries the electric power for the electric motors used to drive the transit cars. This voltage which may typically be 600 volts D.C., although specific systems may have substantially different voltages. The maintenance crews performing work in the vicinity of third rails must have the power turned off on the third rail to avoid an intolerably dangerous working condition. The power to the third rail is typically turned on and off from a remote panel which is not visible to the maintenance crew working near or on the rails.
Maintenance crews have previously relied on make-shift means for determining if a voltage is present on the third rail. These make-shift means have included the use of five conventional incandescent lamps connected in a series. This approach has been unsatisfactory because a single failure of any one of the lamps produced a visual signal which was identical to the signal when no voltage was present. More specifically, although an illuminated string of incandescent lamps connected between one running rail and the third rail indicates electrical power is present, an unlighted string of lamps indicates; (1) no voltage is present or (2) that one or more of the lamps has a burned out filament or (3) there is a bad connection to one of the rails.
A hazard involved in using such apparatus is that the user typically must approach rather closely to the third rail which may be at a relatively high voltage. The high voltage is sufficiently dangerous so that even a slight brush against the third rail may be fatal.
Other problems with these approaches include (1) the test is only a valid test at the instant at which the test is being conducted. In other words, the test is not a continuing test which would produce a very positive signal for the maintenance crew immediately upon turning on power to the third rail. The test can be completed in one instant and an instant later the power can be turned back on and there will be no indication of the power being turned on to warn the maintenance worker that a dangerous voltage level is present on the third rail. Particularly with the light bulb approach, the warning signal is merely a visual signal. It is a continuous test but has two problems: a) bank lights, mainly bulbs, going dead; and b) 625 V D.C. activated (Prior Art FIGS. 1 and 2).
Numerous innovations for third rail warning systems have been provided in the prior art that are adapted to be used. Even though these innovations may be suitable for the specific individual purposes to which they address, they would not be suitable for the purposes of the present invention as heretofore described.